We use the past continuous...1. ... to describe a background scene in a story or in a description of a main event.
2. ... to talk about an action that was in progress when another action took place
(for the shorter action, which happened while the longer one was in progress, we use the past simple)
Examples:1. At 7 a.m. Doug
was having breakfast. He
was sitting at the table and he
was drinking coffee.
2. When he was finishing his breakfast, Meg came into the kitchen